ALD apparatus and method

ABSTRACT

Improved apparatus and method for SMFD ALD include a method designed to enhance chemical utilization as well as an apparatus that implements lower conductance out of SMFD-ALD process chamber while maintaining full compatibility with standard wafer transport. Improved SMFD source apparatuses ( 700, 700′, 700 ″) and methods from volatile and non-volatile liquid and solid precursors are disclosed, e.g., a method for substantially controlling the vapor pressure of a chemical source ( 722 ) within a source space comprising: sensing the accumulation of the chemical on a sensing surface ( 711 ); and controlling the temperature of the chemical source depending on said sensed accumulation.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the field of atomic layer deposition (“ALD”),and more particularly to apparatus and methods for performing ALD withhigh throughput and low cost.

2. Description of Prior Art

Thin film deposition is commonly practiced in the fabrication ofsemiconductor devices and many other useful devices. An emergingdeposition technique, atomic layer deposition (ALD), offers superiorthickness control and conformality for advanced thin film deposition.ALD is practiced by dividing conventional thin-film deposition processesinto single atomic-layer deposition steps, named cycles, that areself-terminating and deposit precisely one atomic layer when conductedup to or beyond self-termination exposure times. The deposition percycle during an ALD process, the atomic layer, typically equals about0.1 molecular monolayer to 0.5 molecular monolayer. The deposition ofatomic layer is the outcome of a chemical reaction between a reactivemolecular precursor and the substrate. In each separate ALDreaction-deposition step, the net reaction deposits the desired atomiclayer and eliminates the “extra” atoms originally included in themolecular precursor.

In ALD applications, typically two molecular precursors are introducedinto the ALD reactor in separate stages. Adequate ALD performancerequires that different molecular precursors are not allowed to intermixwithin the deposition chamber, at the same time. Accordingly, thereaction stages are typically followed by inert-gas purge stages thateliminate the molecular precursors from the chamber prior to theseparate introduction of the other precursor.

During the ALD process, films can be layered down in equal meteredsequences that are all identical in chemical kinetics, deposition percycle, composition, and thickness. This mechanism makes ALD insensitiveto transport nonuniformity resulting in exceptional thickness control,uniformity and conformality.

If ALD is to become commercially practical an apparatus capable ofchanging the flux of molecular precursors from one to the other abruptlyand fast needs to be available. Furthermore, the apparatus must be ableto carry this sequencing efficiently and reliably for many cycles tofacilitate cost-effective coating of many substrates. A useful andeconomically feasible cycle time must accommodate a thickness in a rangeof about from 3 nm to 30 nm for most semiconductor applications, andeven thicker films for other applications. Cost effectiveness dictatesthat substrates be processed within 2 minutes to 3 minutes, which meansthat ALD cycle times must be in a range of about from 5 seconds to 0.5seconds and even less. Multiple technical challenges have so farprevented cost-effective implementation of ALD systems and methods formanufacturing of semiconductor devices and other devices.

Given the need for short cycle times, chemical delivery systems suitablefor use in ALD must be able to alternate incoming molecular precursorflows and purges with sub-second response times. The need to achieveshort cycle times requires the rapid removal of these molecularprecursors from the ALD reactor. Rapid removal in turn dictates that gasresidence time in the ALD reactor be minimized. Gas residence times, τ,are proportional to the volume of the reactor, V, the pressure, P, inthe ALD reactor, and the inverse of the flow, Q, τ=VP/Q. Accordingly,lowering pressure (P) in the ALD reactor facilitates low gas residencetimes and increases the speed of removal (purge) of chemical precursorfrom the ALD reactor. In contrast, minimizing the ALD reaction timerequires maximizing the flux of chemical precursors onto the substratethrough the use of a high pressure within the ALD reactor. In addition,both gas residence time and chemical usage efficiency are inverselyproportional to the flow. Thus, while lowering flow will increaseefficiency, it will also increase gas residence time.

Existing ALD apparatuses have struggled with the trade-off between theneed to shorten reaction times and improve chemical utilizationefficiency, and on the other hand, the need to minimize purge-gasresidence and chemical removal times. Thus, a need exists for an ALDapparatus that can achieve short reaction times and good chemicalutilization efficiency, and that can minimize purge-gas residence andchemical removal times.

Existing ALD apparatuses have also struggled with performancedeterioration caused by extensive growth of inferior films on the wallsof the ALD chambers. This performance deterioration facilitated shortequipment uptime and high cost of maintenance. Thus, a need exists foran ALD apparatus that can minimize the growth of deposits and minimizetheir impact on performance therefore facilitating substantially longeruptime and reduce the cost of maintenance.

Existing ALD apparatuses have struggled with performance deteriorationrelated to slit-valve induced asymmetry with its unavoidable dead-legcavity. The art of single wafer deposition presents a variety ofeffective remedies for this problem. For example, U.S. Pat. No.5,558,717 teaches the advantageous implementation of an annular floworifice and an annular pumping channel. This annular design requires arelatively wide process-chamber design. In another example, U.S. Pat.No. 6,174,377 describes an ALD chamber designed for wafer loading at alow chuck position, while wafer processing is carried out at a highchuck position, leaving the wafer transport channel, and the flowdisturbances associated with it, substantially below the wafer level.Both of these prior art solutions and other prior art solutions are notideally suited to resolve the slot valve cavity problem in ALD systems.

A better solution implements a ring-shaped slit-valve that creates asubstantially symmetric chamber environment. Such embodiment isdescribed in U.S. Pat. No. 6,347,919. However, the ring slit-valvedescribed in U.S. Pat. No. 6,347,919 presents significant performancedeterioration that is associated with the presence of unprotectedelastomeric seals and the respective crevices between the slide of thering slit-valve and the chamber wall that is notorious for entrapment ofchemicals and the growth of deposits and particulates on the seal andwithin the crevices. While deterioration of chamber performance relatedto growth of deposits on slit-valve seals is a universal problem withall existing designs of slit valves, ring-shaped slit-valves as taughtin U.S. Pat. No. 6,347,919 substantially aggravate that problem due tosubstantially longer seals and crevices. Unfortunately, this performancelimitation makes the ring-shaped slit-valve that was taught in U.S. Pat.No. 6,347,919 practically unusable for ALD applications.

A substantial improvement that makes ring-shaped and other perimeterslit-valves suitable and advantageous for ALD applications is describedin U.S. patent application Ser. No. 10/347575, now U.S. Pat. No.6,911,092 issued Jun. 28, 2005, which is commonly assigned to SundewTechnologies, Inc., by the inventor of this invention that provides sealand crevice protection during the ALD chemical dose steps, thereforemaking perimeter slit-valves suitable for Synchronously ModulatedFlow-Draw ALD apparatus and method.

Chemical delivery into ALD chambers has been generally been limited tochemicals with substantial vapor pressure. However, many advantageousALD films rely on molecular precursors that are substantiallynon-volatile. Accordingly existing ALD systems have struggled with thechallenge of consistent chemical delivery of low-volatility molecularprecursors as abruptly shaped doses for promoting high productivity ALDprocesses.

In previous patent applications by the inventor of this invention, U.S.patent application Ser. No. 10/347575, now U.S. Pat. No. 6,911,092issued Jun. 28, 2005, which is commonly assigned to Sundew Technologies,Inc., and PCT Application No. US03/01548, now PCT Publication No. WO03/062490 published Jul. 31, 2003, which is commonly assigned to SundewTechnologies, Inc., embodiments that helped solve some of the problemsdescribed above were disclosed. Systems, apparatuses, and methods inaccordance with that invention provide Synchronous Modulation of Flowand Draw (“SMFD”) in chemical processes, and in particular, in atomiclayer deposition processes and systems. These patent applications areincluded here as references.

Atomic layer deposition (“ALD”) is preferably practiced with the highestpossible flow rate through the deposition chamber during purge, and withthe lowest possible flow rate during dosage of chemicals. Accordingly,an efficient ALD system in accordance with U.S. patent application Ser.No. 10/347575, now U.S. Pat. No. 6,911,092 issued Jun. 28, 2005, whichis commonly assigned to Sundew Technologies, Inc., and PCT ApplicationNo. US03/01548, now PCT Publication No. WO 03/062490 published Jul. 31,2003, which is commonly assigned to Sundew Technologies, Inc., is ableto generate and accommodate

significant modulation of flow rates. Under steady-state conditions, theflow of process gas (either inert purge gas or chemical reactant gas)into a chamber, referred to herein as “flow”, substantially matches theflow of gas out of a chamber, referred to herein as “draw”.

An important aspect of an embodiment in accordance with the inventiondescribed in U.S. patent application Ser. No. 10/347575, now U.S. Pat.No. 6,911,092 issued Jun. 28, 2005, which is commonly assigned to SundewTechnologies, Inc., and PCT Application No. US03/0 1548, now PCTPublication No. WO 03/062490 published Jul. 31, 2003, which is commonlyassigned to Sundew Technologies, Inc., is that it resolves the trade-offin conventional ALD systems between the contradictory requirements of ahigh flow rate during a purge of the deposition chamber and of a lowflow rate during chemical dosage. SMFD in accordance with that inventionprovides the ability to purge a process chamber at a low-pressure and ahigh purge-gas flow rate, and sequentially to conduct chemical dosage inthe process chamber at a high-pressure and a low flow rate of chemicalreactant gas, and to modulate pressures and gas flow rates with fastresponse times.

While the SMFD-ALD device disclosed in the prior applications of thisinventor is a significant improvement in the deposition art, in somerespects the design still reflects the technology available inconventional deposition processes it would be highly useful to have animproved process chamber that takes better advantage of the SMFDprocess, and more fully develops chemical utilization efficiencies. Italso would be useful to provide SMFD-ALD chemical source designs betteradapted to the SMFD process, especially for the efficient and consistentdelivery of vapor from low-volatility liquid and solid chemicals.

SUMMARY OF THE INVENTION

Embodiments in accordance with the invention provide improved apparatusand method to further enhance the advantages of SMFD-ALD apparatus andmethod. In one embodiment, the invention provides a method of conductingatomic layer deposition with enhanced material utilization efficiency.In that method, chemical dosage is conducted in a dose and hold mode.During the hold mode, the flow of chemical into the process chamber isterminated while the flux is effectively maintained. This mode isbeneficial for the final stages of chemical dose where chemicaldepletion is minimal, while maintaining chemical flux can furtherpromote the reaction far into saturation to much improve film quality.

In one aspect a method in accordance with the invention comprisesconducting a chemical dose stage. The chemical dose stage includesfirstly flowing a chemical reactant gas to substantially fill up adeposition chamber, secondly the stage includes substantially reducingthe flow of the chemical reactant gas while concurrently reducing theflow out of the deposition chamber by increasing the pressure downstreamto the deposition chamber to substantially match the flow out of thedeposition chamber to the chemical reactant gas flow into the depositionchamber. Thirdly, terminating the flow of the chemical into thedeposition chamber while concurrently substantially matching thepressure downstream from the deposition chamber to the pressure in thedeposition chamber to substantially suppress the flow out of thedeposition chamber and continuing the chemical dose stage for aspecified time without further introduction of chemical flow. This modeof conducting chemical dose during SMFD-ALD process is in-particularadvantageous when the pressure downstream to the deposition chamber ispreferably increased by flowing gas into a draw gas introduction chamber(DGIC) located in serial fluidic communication downstream from thedeposition chamber.

Improved ALD performance is also described in terms of apparatus andmethod to apply a seal-protected slot valve to control the flowrestriction properties of the ALD space. According to the invention anALD system comprises an improved perimeter slot valve (PSV) in a reactorvessel includes a substrate-transport slot through the reactor-vesselwall (852), a continuous perimeter cavity (854) within thereactor-vessel wall, a continuous sealing poppet (856′) and an actuator(858) for moving the sealing poppet between an open position and aclosed position. The sealing poppet is moved into the perimeter cavityin the closed position, and out of the perimeter cavity in the openposition. The substrate-transport slot is substantially coplanar with asubstrate-supporting surface of the substrate holder and the perimetercavity is substantially coplanar with the substrate-transport slot. Thesubstrate-transport slot defines a substrate-transport channel throughthe reactor-vessel wall to the substrate holder when the sealing poppetis in the open position and separates the substrate-transport slot fromthe vessel interior when the sealing poppet is in the closed position.The improved seal-protected PSV comprises a fixed upper sealing surface,an upper poppet sealing surface corresponding to the fixed upper sealingsurface, an upper peripheral seal, a fixed lower sealing surface, alower poppet sealing surface corresponding to the fixed lower sealingsurface and a lower peripheral seal. According to an important aspect ofthe invention the upper sealing surfaces, the lower sealing surfaces,and the peripheral seals are configured to seal the vessel interior whenthe sealing poppet is in the closed position. In this embodiment, thesubstrate holder is larger than the substrate and the perimeter area ofthe substrate holder is not covered by the substrate, as a result thesealing poppet creates a substantially peripheral narrow gap between theuncovered perimeter area of the substrate holder and the bottom surfaceof the poppet when the seal-protected-PSV is in the closed positionwhere the peripheral narrow gap is narrower than the substrate transportslot when the PSV is in the closed position but the radial narrow gap iswider than the substrate transport slot when the PSV is in the openposition. In many implementations of the invention, the gap controllingPSV is preferably radially shaped. Most importantly is that theimplementation of SMFD-ALD apparatus design with a DGIC and the SMFD-ALDmethod enables seal-protected PSV implementation that is suitable andlow-maintenance. In a preferred design in accordance with the invention,the bottom surface of the poppet is preferably designed with asubstantially down-looking convex shape. Additional improvement taughtby the invention utilizes a purge gas that is preferably introduced atsubstantially low flow between the fixed upper sealing surface and theupper poppet sealing surface to protect the upper sealing surface. Inyet another improvement a PSV also includes a peripheral inflatable sealthat is preferably formed between the fixed upper sealing surface andthe upper poppet sealing surface and the seal is preferably inflatedwhen the PSV is closed to substantially fill-up the downstream from theupper peripheral seal between the fixed upper sealing surface and theupper poppet sealing surface when said inflatable seal is inflated. Inanother improvement the inflatable seal is preferably made from aslightly permeable elastomer and the inflatable seal is inflated withhigh purity inert gas to provide localized purge gas at the area of theinflated seal that is located between the fixed upper sealing surfaceand the upper poppet sealing surface and is exposed to the process. Thislocalized purge substantially protects the exposed area of the seal fromdirectly contacting the process chemicals. Alternatively the inflatableseal is preferably made from a perforated elastomer and the inflatableseal is inflated with high purity inert gas to provide localized purgegas at the area of the inflated seal that is located between the fixedupper sealing surface and the upper poppet sealing surface and isexposed to the process. This localized purge substantially protects theexposed area of the seal from directly contacting the process chemicals.

The invention further teaches and clearly illustrates in the preferredembodiment description and drawings that the bottom surface of thepoppet is advantageously designed with a substantially down-lookingconvex shape to minimize flow disturbances.

Enhanced maintainability of gap-controlling PSV according to anotherembodiment presented in this invention introduces a purge gas atsubstantially low flow between the fixed upper sealing surface and theupper poppet sealing surface of the PSV. This purge gas is suppliedduring processing and protects the inevitable crevice between the poppetand the associated sealing surface from chemical entrapment and thegrowth of inferior film.

Enhanced maintainability of gap-controlling PSV according to yet anotherembodiment presented in this invention utilizes a radial inflatable sealformed between the fixed upper sealing surface and the upper poppetsealing surface of the gap-controlling PSV. According to thisembodiment, the inflatable seal is placed in the gap between the poppetand the corresponding sealing surface, downstream from the upperperipheral radial seal. The seal is preferably inflated when the PSV isclosed to substantially close and eliminate the gap downstream from theupper peripheral seal between the fixed upper sealing surface and theupper poppet sealing surface. In a further enhancement, the inflatableseal is preferably made from a slightly permeable polymer, and theinflatable seal is preferably inflated with high purity inert gas. Theminimal area of the inflated seal that is preferably located between thefixed upper sealing surface and the upper poppet sealing surface andpreferably is exposed to the process and is therefore substantiallypurged by the flow of the high purity inert gas out of the inflatedseal. That flow can be maintained very low to effectively have nodistinguishable impact on SMFD-ALD performance. In another variation inaccordance with the teaching of this invention, the inflatable seal ispreferably made from a perforated polymer and the inflatable seal ispreferably inflated with high purity inert gas. The minimal area of theinflated seal that is located between the fixed upper sealing surfaceand the upper poppet sealing surface and is exposed to the process issubstantially purged by the flow of said inert gas out of the inflatedseal.

The invention also discloses a semi-PSV (SPSV) apparatus for enhancingSMFD-ALD performance. Accordingly, the SPSV includes asubstrate-transport slot through the reactor-vessel wall, a continuousperimeter cavity within the reactor-vessel wall, a continuous sealingpoppet, and an actuator for moving the sealing poppet between an openposition and a closed position. The sealing poppet is moved into theperimeter cavity in the closed position and out of the perimeter cavityin the open position. The substrate-transport slot is preferablysubstantially coplanar with a substrate-supporting surface of thesubstrate holder, and the perimeter cavity is preferably substantiallycoplanar with the substrate-transport slot. The substrate-transport slotpreferably defines a substrate-transport channel through thereactor-vessel wall to the substrate holder when the sealing poppet isin the open position. The sealing poppet preferably separates thesubstrate-transport slot from the vessel interior when the sealingpoppet is in the closed position. Specifically, the SPSV furtherincludes a chamber top, a flexible metal bellow seal or a sliding vacuumseal allowing the chamber top to move up and down while maintainingvacuum integrity, a fixed lower sealing surface, a lower poppet sealingsurface corresponding to the fixed lower sealing surface, and a lowerperipheral seal. The lower sealing surface and the peripheral seal areconfigured to seal the vessel interior when the sealing poppet is in theclosed position. At that position, the poppet essentially defines thetop portion of the vessel. In some SPSV designs the substrate holder ispreferably larger than the substrate, and the perimeter area of thesubstrate holder is not covered by the substrate. The sealing poppetpreferably creates a substantially peripheral narrow gap between theuncovered perimeter area of the substrate holder and the bottom surfaceof the poppet. This peripheral gap is preferably narrower than thesubstrate transport slot when the SPSV is in the closed position and ispreferably equal or wider than the substrate transport slot when theSPSV is in the open position. In important aspects of the invention thechamber top can preferably include a gas distribution showerhead. Thedesign advantageously enhances SMFD-ALD by providing reduced conductancefrom the process chamber into the draw chamber or the DGIC. In oneadvantageous embodiment, the entire ALD manifold is preferably mountedon the moving top of the SPSV and is preferably connected to the processgas and chemical sources with flexible means. In some applications theSPSV preferably has radial symmetry.

In one aspect of the invention an ALD system comprises a perimeter slotvalve (PSV) in a reactor vessel including a substrate-transport slotthrough the reactor-vessel wall, a continuous perimeter cavity withinthe reactor-vessel wall, a continuous sealing poppet and an actuator formoving the sealing poppet between an open position and a closed positionwherein the sealing poppet is moved into the perimeter cavity in theclosed position and out of the perimeter cavity in the open position.The substrate-transport slot is substantially coplanar with asubstrate-supporting surface of the substrate holder, the perimetercavity is substantially coplanar with the substrate-transport slot, thesubstrate-transport slot defines a substrate-transport channel throughthe reactor-vessel wall to the substrate holder when the sealing poppetis in the open position and separates the substrate-transport slot fromthe vessel interior when the sealing poppet is in the closed position.The PSV further includes a fixed upper sealing surface, an upper poppetsealing surface corresponding to the fixed upper sealing surface, anupper peripheral seal, a fixed lower sealing surface, a lower poppetsealing surface corresponding to the fixed lower sealing surface and alower peripheral seal. The upper sealing surfaces, the lower sealingsurfaces and the peripheral seals are configured to seal the vesselinterior when the sealing poppet is in the closed position.Additionally, a plenum for delivering inert gas into the vessel interiorwherein the poppet, the substrate holder and the inert gas deliveryplenum are configured to define a peripheral space when the PSV is inthe closed position and the inert gas is inserted through the inert gasdelivery plenum during chemical dose to substantially reduce the flux ofthe chemical at the surface of the upper seal and the lower seal. Thisseal-protected PSV apparatus and method are preferably suitable for PSVwith radial symmetry as well as any other symmetry.

In another aspect an SMFD-ALD system is disclosed comprising a reactionvessel defined by reaction vessel wall, a translatable liner and anactuator to translate the translatable liner between low and highpositions. This translatable liner preferably includes a substantiallyconvex surface at the bottom portion that creates a peripheral gap whenactuated to the low position creating a substantially symmetricperipheral surface around a substrate holder. The substrate holder ispreferably larger than the substrate and a peripheral DGIC space ispreferably created between the liner, the substrate holder and the wallof the reaction vessel when the liner is at the low position. In furtheraspect the liner preferably comprises a gas plenum to deliver inert gasfrom the upper and the lower peripheral edges of the liner into theperipheral DGIC space and the inert gas is preferably inserted throughthis gas plenum during chemical dose to substantially reduce the flux ofthe chemical at the surface of the upper edge and the lower edge of theliner and their respective crevices. The Apparatus disclosed withrespect to the translatable liner can be preferably selected to haveradial symmetry or other peripheral symmetry.

In yet another improvement this invention discloses an SMFD-ALD systemcomprising an apparatus for high speed draw control gas delivery intoand out-of a DGIC. In a specific aspect the SMFD-ALD system havinghigh-speed draw control gas delivery apparatus comprises an inlet FRE, agas reservoir, A shutoff valve, an outlet FRE all placed in seriesfluidic communication between an inert gas source and the DGIC.Additionally, a pumping line and a pumping shutoff valve provide serialfluidic communication between the outlet FRE and a vacuum pump. Theapparatus is set to shape a time varying inert gas introduction into aparasitic space that is located in serial fluidic communication betweenthe outlet FRE and the DGIC and the time varying inert gas introductionpreferably comprises a high-flow leading edge. To facilitate fastreduction of draw-control flow the parasitic space is preferablyconnected to the vacuum pump concurrently with the shut-off of the inletvalve.

In another aspect an atomic layer deposition system comprising adeposition chamber, a gas draw chamber, a deposition chamber seal havinga seal gap area exposed to the deposition and a gas purge sourceconnected to the seal gap is disclosed.

In another aspect a method of atomic layer deposition comprisesproviding an atomic layer depositing apparatus having a depositionchamber and a deposition chamber seal gap, a portion of which seal gapis exposed to the deposition chamber wherein the method includesdepositing a thin film in the deposition chamber and purging the sealgap portion exposed to the deposition chamber with purge gas during thedeposition is key to maintain the seal and the performance of the ALDsystem.

In another aspect a disclosed atomic layer deposition apparatuscomprises a combination of a deposition chamber housing having a fixedhousing portion and a movable portion and the movable portion issupported on a bellows to maintain vacuum integrity.

In another aspect an atomic layer deposition apparatus comprises adeposition chamber housing having a fixed housing portion and a movableportion, a gap between the fixed housing portion and the movable portionand an inflatable seal for sealing that gap. In a modified aspect theseal is preferably perforated and further includes a source of purge gasconnected to the gap. In another modification the apparatus preferablyincludes a shaped seat against which the seal seats when inflated. Inanother modification the apparatus preferably includes a ferrule locatedinterior to the inflatable seal.

Improvements are also disclosed for SMFD optimized source design.Apparatuses and methods for generic source design are implemented withcommercially available pressure controller for volatile chemicals andwith the aid of newly invented apparatuses for lower-volatilitychemicals. A chemical vapor source for SMFD-ALD apparatus in accordancewith the invention includes a chemical container, a pressure controllerin serial fluidic communication downstream from the chemical container,and a source chamber in serial fluidic communication downstream from thepressure controller. The pressure controller is located in serialfluidic communication upstream from the source chamber. The set pressureof the chemical vapor is maintained in the source chamber by thepressure controller. In one preferred design, the chemical sourcecapacity preferably exceeds the capacity loss per ALD cycle by a factorof 10. In another exemplary design, the chemical source capacitypreferably exceeds the capacity loss per ALD cycle by a factor of 100.

Further, the invention discloses a chemical vapor source for an SMFD-ALDapparatus comprising a liquid delivery system, a vaporizer in serialfluidic communication downstream from that liquid delivery system, and asource chamber in serial fluidic communication downstream from thevaporizer. A set chemical vapor pressure inside the source chamber ismaintained by controlling the liquid delivery into the vaporizer. Thechemical vapor pressure is measured in the source chamber, and theliquid delivery system is controlled to maintain that pressure at theset point. Therefore, the precision and response of the pressure controldepends on the precision of the liquid delivery system and its abilityto respond quickly. In one exemplary embodiment, the chemical sourcecapacity preferably exceeds the capacity loss per ALD cycle by a factorof 10. In another exemplary embodiment, the chemical source capacitypreferably exceeds the capacity loss per ALD cycle by a factor of 100.

Further, an advantageous embodiment for a liquid delivery apparatus isdisclosed, exemplified, and illustrated for clarity. Accordingly, acontrolled flow of liquid through preferably a proportional valve, ametering valve or a fixed orifice is driven by an expandable pressurechamber. The expansion of that expandable pressure chamber protrudesinto a liquid filled chamber. The pressure chamber is separated from theliquid filled chamber with an expandable flexible metallic bellow. Whenthe pressure chamber is inflated, it expands the bellow into theliquid-filled chamber to effectively pressurize the liquid and triggerthe flow. The inflation or deflation operations are controlled with afast solenoid-based valve and the introduction or disposition of airpressure, respectively. Accordingly, liquid flow can be triggered ON orOFF with unprecedented and adequate speed preferably in the range offrom 5 msec to 50 msec response time.

In another aspect of the invention a chemical vapor source for SMFD-ALDapparatus is disclosed comprising a chemical source employing atemperature controlled sensor that senses the accumulation of materialson it's sensing surface to control the vapor pressure of the chemicalwithin a source space. The walls of the source space are preferablymaintained at a temperature that is sufficiently high to preventcondensation of the chemical. Preferably, the sensor is a quartz crystalmicrobalance (QCM) sensor or a SAW device thickness monitor or any othersensor that can sense the accumulation of material on it's sensingsurface. Accordingly, the sensor is applied to control the temperatureof the chemical to continuously maintain a minimal condensation of thechemical over the sensor. In an aspect of this invented chemical sourcethe chemical is preferably loaded into a heatable holder, such ascrucible, and the power to heat the crucible is preferably controlled bythe sensor. In most applications taught by the invention the chemical ispreferably solid. An important design preferably incorporates chemicaldelivery into the crucible as a slurry of fine powder and inert liquidpreferably liquid with low boiling temperature. The inert liquidpreferably does not substantially dissolute the solid chemical and canbe vacuum evaporated away from the chemical source to effectively leavea pure and dry solid chemical inside the crucible. In certainapplication the chemical source taught in this invention preferablyemploys also a combination of pressure gauge and controllable valve tocontrol the total pressure within the source space that exceeds thevapor pressure controlled from the chemical. In that case thecontrollable valve preferably delivers inert gas into the source space.A method and apparatus for increasing the versatility of the source isdisclosed where the controllable valve preferably delivers an etchinggas into the source space and the chemical is preferably generatedwithin the source space. In this aspect controlling the vapor pressureof the chemical preferably means controlling the temperature of anelemental or compound target and/or the temperature of the etchant toinduce sufficient etching and the chemical is essentially the product ofsaid etching. This apparatus and method are especially and preferablyuseful to produce precursors from the elements Hf, Zr, Ru, RuO₂, Si, W,Mo, Co, Cu, Al, Fe, Os, OsO₂ and Ta; and the etching gas preferablyselected from the list of Cl₂, Cl₂/N₂, Cl₂/O₂/O₃, N₂/HF, CO, CO/N₂ andtheir combinations. In another apparatus design, temperature limitationsof pressure gauges are preferably overcome by implementing the chemicalsource using a pressure controlled gas reservoir in series fluidiccommunication upstream from the source space and a shutoff valve placedin series fluidic communication between the pressure controlledreservoir and the source space where the shutoff valve is preferablyused to substantially equalize the total pressure within the sourcespace to the pressure in the pressure controlled reservoir betweensuccessive ALD doses. In this case there is preferably no need toinclude a heatable pressure gauge within the hot zone of the source andthe source useful temperature range is preferably extended beyond thelimitation of pressure gauges. The source that is taught in thisinvention is preferably very useful and adequate for ALD applicationswhen the capacity of the source space is preferably more than 10 timethe capacity required for a single ALD dose and even better suited forALD when the capacity of the source space is preferably more than 50time the capacity required for a single ALD dose. In conjunction withthe chemical source apparatus that is extensively disclosed andexemplified in this invention a complementary method for substantiallycontrolling the vapor pressure of a chemical within a space employing atemperature controlled sensor to measure the condensation rate of thechemical at the sensor's temperature is disclosed. The sensor isemployed to control the evaporation rate of the chemical to maintain aminimal measurable condensation rate while the sensor's temperature isselected to appropriately determine the desired vapor pressure of thechemical. The method is preferably extended to cases that preferablyrequire seeding the chemicals into a carrier gas wherein a totalpressure higher than the vapor pressure of the chemical is preferablycontrolled inside the source space and the balance of gas inside thesource space preferably comprises an inert gas. The method is evenfurther extended to cases that preferably require seeding the chemicalsinto a carrier gas wherein a total pressure higher than the vaporpressure of the chemical is controlled inside the source space and thebalance of gas inside the source space preferably comprises an etchinggas or an etching gas mixture and the desired chemical is preferablygenerated by etching an elemental or compound target while the sensor ispreferably employed to control the generation rate of the desiredchemical to maintain a minimal measurable condensation rate measured onthe sensor. The selected generation rate of the desired chemical ispreferably controlled by controlling the heating of the target and thesensor's temperature is selected to appropriately determine the desiredvapor pressure of the desired chemical.

The invention thus also provides a chemical source vapor pressurecontrol system comprising a deposition chamber, a chemical source holderfor holding the chemical source, a chemical source heater, a sourceheater controller, and a deposition accumulation sensor, the heatercontroller electrically connected to the deposition accumulation sensorto control the heating of the source; the system characterized by: thetemperature controlled deposition accumulation sensor located out ofline-of sight with the chemical source; and a sensor temperature controlunit for controlling the temperature of the accumulation sensor to atemperature lower than the condensation temperature of the chemicalsource at the desired vapor pressure. Preferably, the deposition chamberhas chamber walls (708) and further comprising a chamber walltemperature control system for maintaining the walls at a temperaturethat is sufficiently high to prevent condensation of the chemicalsource. Preferably, the chemical source vapor pressure control systemfurther includes a pressure gauge, a gas control valve, and a pressurecontroller connected between the gauge and the valve to control thetotal pressure within the deposition chamber to a pressure higher thanthe controlled vapor pressure of the chemical source. Preferably, thechemical source vapor pressure control system includes a source of anetch gas connected to the gas control valve, and the sensor senses anetching product. Preferably, the chemical source is selected from thegroup consisting of Hf, Zr, Ru, RuO₂, Si, W, Mo, Co, Cu, Al, Os, OsO₂,Fe, Ta and combinations thereof; and the etching gas is selected fromthe group consisting of of Cl₂, Cl₂/N₂, Cl₂/O₂/O₃, N₂/HF, N₂/ClF₃, CO,CO/N₂ and combinations thereof. Preferably, the chemical source vaporpressure control system further includes a pressure controlled reservoir(780); a shutoff valve (744′) in series fluidic communication betweenthe pressure controlled reservoir and the deposition chamber tosubstantially equalize the pressure between the deposition chamber andthe pressure controlled reservoir between successive ALD doses.Preferably the source is applied for ALD and the capacity of thedeposition chamber is 20 times or more larger than the capacity requiredfor a single ALD dose.

The invention also provides a method for controlling the vapor pressureof a chemical source within a source space the method comprising:sensing the accumulation of the chemical on a sensing surface; andcontrolling the temperature of the chemical source depending on thesensed accumulation. Preferably, the temperature of the chemical sourceis controlled to maintain a minimal measurable condensation rate on thesensing surface. Preferably, the temperature of the sensor is controlledto appropriately determine the desired vapor pressure of the chemical.Preferably, the total pressure in the source space is controlled to behigher than the vapor pressure of the chemical. Preferably, the methodincludes introducing an etching gas into the source space, and etchingan elemental or compound target to produce the chemical.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the invention may be obtained byreference to the drawings, in which:

FIG. 1 depicts a flow diagram of a basic embodiment of a synchronouslymodulated flow-draw (“SMFD”) ALD system in accordance with theinvention;

FIG. 2 depicts in schematic form a comparison between prior art ALDprocess (2 a), SMFD-ALD process (2 b and 2 c), and pulse and holdSMFD-ALD process (2 d);

FIG. 3 depicts schematically a seal-protected perimeter slot valve atthe close position in accordance with the invention;

FIG. 4 depicts schematically a seal protected perimeter slot valve atthe open position in accordance with the invention;

FIG. 5 depicts schematically a gap-controlling perimeter slot valve atthe close position in accordance with the invention;

FIG. 6 depicts schematically a gap-controlling perimeter slot valve atthe open position in accordance with the invention;

FIG. 7 highlights the seal area of a gap-controlling perimeter slotvalve showing the seal purge line;

FIG. 8 depicts schematically a semi-perimeter slot valve at the closeposition in accordance with the invention;

FIG. 9 highlights in schematic form a design for inflatable seal elementshown deflated in accordance with the invention;

FIG. 10 highlights in schematic form a design for inflatable sealelement shown inflated in accordance with the invention;

FIG. 11 illustrates the inflatable seal assembly (with reference to FIG.10) in accordance with the invention;

FIG. 12 illustrates the inflatable seal assembly (with reference to FIG.10) showing the inflation gas line and the connection with theinflatable seal in accordance with the invention;

FIG. 13 depicts the same inset as in FIG. 12 where the seal is showninflated in accordance with the invention;

FIG. 14 depicts a translatable liner in accordance with the invention;

FIG. 15 depicts a flow diagram of a basic embodiment of a synchronouslymodulated flow-draw (“SMFD”) ALD system comprising a sub-manifold forhigh-speed introduction and removal of draw control flow in accordancewith the invention;

FIG. 16 depicts schematically a pressure-controlled source for gas andvolatile liquid and solid precursors in accordance with the invention;

FIG. 17 depicts schematically a pressure-controlled source fornon-volatile liquid precursors in accordance with the invention;

FIG. 18 depicts schematically a liquid delivery source in accordancewith the invention.

FIG. 19 depicts schematically a chemical source implementing a sensorthat monitors the accumulation of materials such as a QCM for themeasurement and control of chemical vapor pressure in accordance withthe invention;

FIG. 20 depicts schematically a chemical source implementing a QCM forthe measurement and control of chemical vapor pressure and anindependent total pressure control in accordance with the invention;

FIG. 21 depicts schematically a chemical source implementing a QCM forthe measurement and control of chemical vapor pressure using an etchtarget and an independent total pressure control in accordance with theinvention; and

FIG. 22 depicts schematically a chemical source implementing a QCM forthe measurement and control of chemical vapor pressure using an etchtarget and an independent total pressure replenishing apparatus inaccordance with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention is described herein with reference to FIGS. 1-22. For thesake of clarity, the same reference numerals are used in several figuresto refer to similar or identical components. It should be understoodthat the structures and systems depicted in schematic form in FIGS. 1-22serve explanatory purposes and are not precise depictions of actualstructures and systems in accordance with the invention. Furthermore,the embodiments described herein are exemplary and are not intended tolimit the scope of the invention, which is defined in the inventionsummary and in the claims below.

FIG. 1 depicts a flow diagram of a basic embodiment of a synchronouslymodulated flow-draw (“SMFD”) ALD system 600 in accordance with theinvention described in U.S. patent application Ser. No. 10/347575, nowU.S. Pat. No. 6,911,092 issued Jun. 28, 2005, which is commonly assignedto Sundew Technologies, Inc., POT Application No. US03/01548, now PCTPublication No. WO 03/062490 published Jul. 31, 2003, which is commonlyassigned to Sundew Technologies, Inc., and the improvements that aredisclosed in this application.

System 600 comprises a pressure-stabilized inert, purge-gas source 602of a purge gas 604. Purge gas is supplied through purge-source shut-offvalve 102 and purge-source flow restriction element (“FRE”) 103 into gasdistribution chamber 104, which is commonly a conventional shower head.As depicted in FIG. 1, purge-source shut-off valve 102 and purge-sourceFRE 103 provide serial fluidic communication between purge-gas source602 and gas distribution chamber 104. In this specification, flowrestriction elements (FREs) cause a pressure step-down when gas isflowing through them. A chemical reactant precursor in the form of apure chemical gas, a vapor from a liquid or solid chemical, or mixturesof vapor or gas chemicals with inert gas is provided at well-controlledpressure at a plurality of chemical-gas sources 105, 105′. Chemical-gassource 105 is connected in serial fluidic communication with boosterchamber 107 through chemical-source-FRE 106. Booster chamber 107 isconnected in serial fluidic communication with gas distribution chamber(showerhead) 104 through chemical-dosage shut-off valve 110 andbooster-FRE 109. As depicted in FIG. 1, second chemical-gas source 105′is connected to showerhead 104 with devices corresponding to thosedescribed with reference to chemical-gas source 105.

Gas-distribution FRE 113 provides serial fluidic communication betweengas distribution chamber 104 and atomic layer deposition chamber(“deposition chamber”) 114. In a preferred embodiment, in which gasdistribution chamber 104 is a showerhead device, gas-distribution FRE113 is commonly a nozzle array. A nozzle array provides restricted anduniform flow from gas distribution chamber 104 to deposition chamber114, which contains a substrate being treated. A substrate supportingchuck with means to control the substrate temperature, 620, is disposedwithin deposition chamber 114.

Deposition chamber 114 is connected in serial fluidic communication to asmall-volume draw-gas introduction chamber (“DGIC”) 630 throughdeposition-chamber FRE 115. Inert draw-gas source 602 is connected inserial fluidic communication to DGIC 630 through draw-gas line 119,draw-source shut-off valve 120, and draw-source-FRE 121. Draw-gasintroduction chamber 630 is connected in serial fluidic communicationthrough DGIC-FRE 632 to draw control chamber (“DC”) 116. A chemicalabatement element 634 is disposed inside DC 116. DC 116 is connected inserial fluidic communication to pump chamber 636 through draw-controloutlet 124 and draw-control FRE 117. A pressure gauge 638 is connectedto DC 116. Pressure gauge 638, for example, an MKS Baratron model 628type, monitors the process through, for example, the average pressure inDC 116. Similarly, other process monitoring devices (not shown), such asgas analyzers, can be conveniently connected to DC 116. Low pressuregauge 644, such as an HPS I-Mag cold-cathode gauge, is attached to pumpchamber 636 to monitor chamber pressure during idle time. Turbomolecularpump 640 is connected to pump chamber 636 through a pumping gate-valve642 to facilitate high vacuum during idle time and high-throughput flowduring ALD operation. For example, a pump selected from the BOC-EdwardsSTPA series is suitable. Good performance for ALD deposition on 200 mmsilicon wafers was obtained using an STPA 1303C pump. Turbomolecularpump 640 is evacuated using backing pump 646. For example, a BOC EdwardsQDP40 or equivalent serves well as backing pump 646. In otherembodiments in accordance with the invention, higher pumping-speed pumparrangements, such as the QMB series from BOC Edwards, facilitate remotelocation placement of dry pumps, as known in the art.

In certain preferred embodiments, reactive gas is added to DC 116 toenhance chemical abatement. Accordingly, system 600 comprises anozone-supply manifold. Oxygen, oxygen-argon or oxygen-nitrogen mixturesare supplied from gas cylinder 650. A mass flow controller 652 controlsthe flow of gas into a commercially available ozone generator 654. Forexample, the MKS Astex AX8407 series ozone generators perform well inSMFD system 600. The output from ozone generator 654 is monitored byozone monitor 656, allowing feedback-control stabilization of ozoneconcentrations. Pressure controller 658, for example, an MKS 640A type,maintains a selected constant pressure inside ozone generator 654. Forthe purpose of pulsing ozone into DC 116 while maintaining controlledflow and pressure that are necessary for correct operation of ozonegenerator 654, an ozone reservoir 660 comprises a volume selected tosuppress the impact of ozone pulsing on the pressure inside ozonegenerator 654. This allows pulsing of reactive ozone into DC 116, whilemaintaining a desired flow and pressure in ozone generator 654. Pressurecontroller 662 controls the pressure in ozone reservoir 660. Ozonedegradation is minimized in system manifold 600 by maintaining the ozonesupply manifold at substantially room temperature and by minimizing thestagnant volume between ozone generator 654 and DC 116. For example, thestagnant volume is described schematically in FIG. 1 by the dead-legbetween valve 664 and junction 668. Ozone is fed to ozone shut-off valve664 and ozone-source FRE 666 through the inner tubing of a double-wallline and fed to the inlet of pressure controller 662 by the return flowbetween the inner and the outer tubing. In this manner, the impact ofozone depletion in the stagnant space is minimized by reducing thedead-leg between valve 664 and junction 668 to less than 1 cc.Preferably, an ozone-eliminating catalytic converter 670 is disposed atthe outlet of pump 642 to suppress ozone emission to the ambient.

In a preferred embodiment, the functionality of chemical-dosage shut-offvalves 110, 110′ was integrated into a multiple-port chemicalintroduction valve manifold comprising both 110 and 110′. Fast pneumaticvalves with millisecond response time, described in a separate patent bythe inventor of this invention were mainly utilized successfully forthat purpose.

During typical ALD operation, apparatus 600 is switched essentiallybetween two static modes, a purge mode (“purge”) and a chemical-dosagemode (“dose”). Representative valve-settings of the two basic modes ofoperation are presented in Table 1. More teaching about the SMFD ALDapparatus and method is given in U.S. patent application Ser No.10/347575, now U.S. Pat. No. 6,911,092 issued Jun. 28, 2005, which iscommonly assigned to Sundew Technologies, Inc., and PCT Application No.US03/01548 , now PCT Publication No. WO 03/062490 published Jul. 31,2003, which is commonly assigned to Sundew Technologies, Inc.

TABLE 1 Mode Valve 102 Valve 120 Valve 110 Purge OPEN CLOSED CLOSEDChemical dosage CLOSED OPEN OPEN

FIGS. 2 present a schematic comparison between prior art flow versustime chart 300 presented in FIG. 2 a and the inlet flow into an SMFDshowerhead 104, chart 320 presented in FIG. 2 b. Since typical SMFDtiming is more than 5 times shorter, the time scale of the SMFD chartsis divided by a factor of 5. FIG. 2 c presents chart 340 whichrepresents the complementary flow versus time into the DGIC 630 insynchronization with the inlet flow depicted in chart 320 (FIG. 2 b ).An ALD cycle comprised of first chemical dose 302, first purge 304,second chemical dose 306, and second purge 308 is conventionally carriedunder substantially constant flow conditions as illustrated in chart300. In contrast, the inlet sequence 320 of first chemical dose 322,first purge 324, second chemical dose 326, and second purge 328 iscarried under substantially modulated flow conditions. Complementarydraw flow presented in chart 340 maintains the pressure during chemicaldose steps with draw flow 342 and 344 during chemical dose steps 322 and326, respectively. Note the transient stages 321 and 325 at the leadingedge of chemical dose 322 and 326, respectively. These booster high-flowleading edge transients are further taught in U.S. patent applicationSer. No. 10/347575, now U.S. Pat. No. 6,911,092 issued Jun. 28, 2005,which is commonly assigned to Sundew Technologies, Inc., and PCTApplication No. US03/101548, now PCT Publication No. WO 03/062490published Jul. 31, 2003, which is commonly assigned to SundewTechnologies, Inc.

A further improvement in chemical utilization splits the chemical dosesteps into pulse and hold in accordance with Table 2.

TABLE 2 Mode Valve 102 Valve 120 Valve 110 Purge OPEN CLOSED CLOSEDChemical dose PULSE CLOSED OPEN OPEN Chemical dose HOLD CLOSED OPENCLOSED

This improvement is depicted in FIG. 2 d. The flow versus time isillustrated in chart 360. Accordingly, the first chemical dose includestransient 361, low flow steady-state 362, and no flow period 363.Similarly, the second chemical dose includes transient 365, low flowsteady-state 366, and no flow 367. When valve 110 shuts off during thedose, the flow into the deposition chamber ceases. The depositionchamber becomes a dead-leg and the pressure in deposition chamber 114transients down slightly to match the pressure in DGIC 630. If chemicaldepletion is not prominent, dose time is extended at no additionalincrease in chemical utilization. This improved mode of chemical dosecan be utilized to improve the quality of ALD films by extendingchemical reaction time to facilitate further completion of thesereactions. The global rate of the typically first order ALD reactions isproportional to the flux of chemicals and concentration of unreactedsites. Naturally, as the reaction propagates, the number of reactivesites decreases and accordingly the global reaction rate decreases. Inmany ALD processes, the inevitable residual concentration of reactivesites that is not reacted at the end of the chemical dose stepcontributes to the inclusion of impurities in the film. In particular,embedded OH groups are detrimental to insulating properties ofdielectric ALD films. Therefore, in some ALD processes, film quality mayrequire extended chemical dose exposures. The pulse and hold mode givenin Table 2 and illustrated in chart 360 advantageously extends theactual dose exposure while avoiding the penalty of increasing chemicalutilization. For example, trimethylaluminum (TMA) dose of 50 msec wasutilized with only 10 msec to 20 msec of pulse and complementary 30 msecto 40 msec of hold on our SMFD system. The pulse and hold mode furtherimproves chemical utilization efficiencies by eliminating any pressuregradients in deposition chamber 114 during the HOLD time. Thisdecoupling between the exposure (flux multiplied by dose time) and theutilization of chemical is a key advantage of pulse-and-hold SMFD.

The pulse-and-hold mode enables efficient chemical utilization duringlow temperature ALD. ALD reactions are thermally activated. At lowtemperatures, ALD reactions are slow and inefficient. To minimize dosetimes, ALD precursors are dosed at maximized pressure and 100%concentration. Pulse and hold SMFD mode is advantageously implemented tosuppress the loss of chemical during dose. A pulse and hold sequence wasimplemented for TMA dose during SMFD-ALD of Al₂O₃ at 100° C. A fullysaturated process step required only 20 msec of pulse and 30 msec ofdose (total of 50 msec dose time). Material utilization was greater than5%, which is extremely good for such low temperature process that wasexecuted with such short dose time.

A useful range for dose was attempted successfully between 5 msec to 120msec, and a useful range of hold was tested from a minimum of 5 msec upto 200 msec. Preferably, dose is carried with a 5 msec to 50 msecduration, and hold is carried with a 20 msec to 100 msec duration.Mostly a preferred range of 5 msec to 25 msec for dose and 15 msec to 35msec for hold is recommended.

FIGS. 3 and 4 depict in schematic form a cross-section of a preferredALD reactor vessel 800. As shown in FIG. 3, reactor vessel 800 comprisesa reactor-vessel wall 802, a reactor-vessel top 804, and a vessel-bottom806, which define a vessel interior 808. Reactor vessel 800 includes gasdistribution chamber (showerhead) 201. A showerhead inlet 809 at top 804serves as an inlet for chemical reactant gases and purge gases intoshowerhead 201. Nozzle array flow restricting element (FRE) 202separates the bottom of gas distribution chamber 201 from ALD depositionchamber (process chamber) 203. A substrate 204 is supported on heatedwafer chuck (substrate holder) 205, made from a thermally conductingmetal (e.g., W, Mo, Al, Ni) or other materials commonly used in the artfor hot susceptors and chucks. Wafer chuck 205 includes a wafer lift-pinmechanism 810. Wafer transport is accomplished with aid of lift pins 812(only one out of three pins shown), as known in the art. Wafer lift pins812 are actuated to lift wafer substrate 204 above the top surface ofchuck 205 using actuator 814 and levitation arm 816. Deposition chamber203 is confined by deposition-chamber FRE 206 representing a typicallyperipheral passage between top 804 and chuck 805. A draw-gasintroduction chamber (“DGIC”) 820 is located downstream from depositionchamber 203, between FRE 206 and DGIC-FRE 822. A draw control chamber(“DC”) 208 is located downstream from DGIC, and is confined by DGIC-FRE822 and draw-control FRE baffle 209. Chemical-abatement element 824 isdisposed inside DC 208. Spacer 826 provides direct thermal contact ofchemical-abatement element 824 and draw-control FRE baffle 209 withheated wafer chuck 205.

Draw-gas inlet 830 provides serial fluidic communication between adraw-gas manifold (not shown) and a draw gas plenum 832. One skilled inthe art can implement draw gas plenum 832 in many differentconfigurations, and the embodiment shown in

FIGS. 3 and 4 is a non-exclusive example. As depicted in FIG. 3,draw-gas inlet 830 is in fluidic communication with radial plenum space832, which further communicates with DGIC 820 through a radial array ofnozzles (not shown), which are appropriately spaced and designed tounify the radial flow distribution of gas into DGIC 820 and direct drawgas into the upstream portion of DGIC 820. Those who are skilled in theart can appreciate the necessity to adequately unify the flow of drawgas and reactive abatement gas to conform to the symmetry of thedeposition system. For example, the radial symmetry of the system isdepicted in FIGS 3 and 4. Indeed, a draw control gas, introduced with asubstantially non-uniform radial distribution, impacted the radialdistribution of dosed chemicals as observed when ALD was tested with oneof the dose steps kept under saturation conditions. While saturationproperties of ALD reaction steps can overcome this effect, longerchemical doses are dictated that, in turn, extend the ALD cycle time andin many cases reducing the chemical utilization efficiency. As explainedin U.S. patent application Ser. No. 10/347575. now U.S. Pat. No.6,911,092 issued Jun. 28, 2005, which is commonly assigned to SundewTechnologies; Inc., and PCT Application No. US03/01548, now PCTPublication No. WO 03/062490 published Jul. 31, 2003, which is commonlyassigned to Sundew Technologies. Inc., and further below, the drawcontrol gas, the DGIO and the SMFD method are crucial and instrumentalin enabling the implementation of perimeter slit-valve to improveperformance and reduce the size of the ALD chamber. In that respect, theplenum and the DGIC protect the seals of the PSV and their respectivecrevices from a substantially damaging contact with the processchemicals.

Optionally, reactive gas is delivered from a reactive gas manifold (notshown) through line 840 into reactive-gas plenum 842. Reactive-gasplenum 842 serves to shape a uniform radial flow distribution ofreactive abatement gas into draw chamber 208. For example, the reactivegas is delivered into a radial channel that communicates with drawchamber 208 through a plurality of horizontal nozzles that areappropriately spaced and designed. One skilled in the art can appreciatethat reactive gas plenum system 842 can be implemented in many differentconfigurations in accordance with the invention.

During ALD processing, purge gas during a purge stage and chemicalreactant gas during a dosage stage flow along a process-gas flow-paththrough reactor-vessel interior 808 in a downstream direction fromshowerhead inlet 809 through showerhead 201, deposition chamber 203,DGIC 820, and DC 208, in that order, and out of reactor vessel 800through vacuum port 210. Similarly, draw gas introduced into DGIC 820flows in a downstream direction from DGIC 820 into DC 208 and then exitsthrough vacuum port 210. The terms “downstream” and “upstream” are usedherein in their usual sense. It is a feature of embodiments inaccordance with the invention that backflow of gases, that is, the flowof gases in an “upstream” direction, never occurs, as taught in U.S.patent application Ser. No. 10/347575, now U.S. Pat. No. 6,911,092issued Jun. 28, 2005, which is commonly assigned to Sundew Technologies,Inc., and PCT Application No. US03/01548 now PCT Publication No. WO03/062490 published Jul. 31, 2003, which is commonly assigned to SundewTechnologies, Inc. The term “upstream” is used in this specification,however, to designate the relative locations of components and parts ofa system.

Reactor vessel 800 further includes a perimeter slot valve (“PSV”) 850.As depicted in FIGS. 3 and 4, PSV 850 comprises a substrate-transportslot 852 through reactor-vessel wall 802, a continuous perimeter cavity854 (FIG. 4) within reactor-vessel wall 802, a continuous sealing poppet856, and an actuator 858 for moving sealing poppet 856 between an openposition (FIG. 4) and a closed position (FIG. 3). Sealing poppet 856 ismoved into perimeter cavity 854 in the closed position (FIG. 3), andsealing poppet 856 is moved out of perimeter cavity 854 in the openposition (FIG. 4). Substrate-transport slot 852 is substantiallycoplanar with the substrate-supporting surface of substrate holder 205.Perimeter cavity 854 is substantially coplanar with substrate-transportslot 852. Substrate-transport slot 852 defines a substrate-transportchannel through reactor-vessel wall 802 to substrate holder 205 whensealing poppet 856 is in open position (FIG. 4), and sealing poppet 856separates substrate-transport slot 852 from vessel interior 808 whensealing poppet 856 is in its closed position (FIG. 3).

Reactor-vessel wall 802 defines a vessel perimeter within thereactor-vessel wall, and sealing poppet 856 conforms to the vesselperimeter when sealing poppet 856 is in its closed position (FIG. 3). Asdepicted in FIGS. 3 and 4, reactor-vessel wall 802 comprises asubstantially radially symmetric shape, and sealing poppet 856 comprisesa substantially radially symmetric shape in the case wherein the chambersymmetry is substantially radial. It is understood that otherembodiments of reactor vessel 800 and PSV 850 in accordance with theinvention could have other geometric shapes. As depicted in FIG. 3,sealing poppet 856 in its closed position forms an inner sealing wall862 of the process-gas flow-path in vessel interior 808. Inner sealingwall 862 comprises a radially symmetrical shape, which promotes aradially symmetric flow of gasses along the process-gas flow-path and,thereby, enhances uniform deposition and reduces formation of soliddeposits. In the particular embodiment of reactor vessel 800 as depictedin FIG. 3, a portion of inner sealing wall 862 defines a portion of DGIC820. As depicted in FIG. 4, PSV 850 comprises a fixed upper sealingsurface 870, an upper poppet sealing surface 872 corresponding to fixedupper sealing surface 870, an upper peripheral seal 873, a fixed lowersealing surface 874, a lower poppet sealing surface 876 corresponding tofixed lower sealing surface 874, and a lower peripheral seal 877. Uppersealing surfaces 870, 872, lower sealing surfaces 874, 876, andperipheral seals 873, 877 are configured to seal the vessel interiorwhen sealing poppet 856 is in its closed position (FIG. 3).

As depicted in FIG. 4, upper peripheral seal 873 and lower peripheralseal 877 are assembled on poppet sealing surfaces 872, 876,respectively. Also, seals 873, 877 are configured as o-ring seals. It isclear that different types of seals, for example, flat gasket seals, areuseful, and that seals 873, 877 can be assembled on fixed sealingsurfaces 870, 874, instead of on poppet sealing surfaces 872, 876.Suitable materials for seals 873, 877 include elastomer materials madefrom Viton, Kalrez, Chemraz, or equivalents. One skilled in the art iscapable of implementing perimeter slot valve 850 in many differentconfigurations.

Substrate-transport slot 852 and the associated wafer transport systemcommunicated through slot 852 are completely isolated from the ALDprocess system in reactor vessel interior 808 when PSV 850 is closed.

The implementation of the preferred embodiment has revealed that indeedthe high flow of inert gas into the leading edge of the DFIC duringchemical dose was sufficient to provide exceptional protection againstpossible film buildup in radial crevices 882 and 884 that are formedbetween 804 and 856 and between 856 and 802, respectively. Accordingly,seal-protected PSV was implemented with no adverse impact on maintenancecycle or performance. These adverse effects are typical and practicallimitations in the case of a simple ring-shaped slit-valveimplementation as taught in U.S. Pat. No. 6,347,919. Additionalimprovements that enable the implementation of perimeter slit-valve inALD apparatuses and other processing chamber are taught in an additionalpatent by the inventor of this invention.

The PSV can be further utilized to reduce the conductance of FRE 115between process chamber 114 and DGIC 630 (FIG. 1). Smaller FRE 115conductance increases the pressure gradient between process chamber 114and DGIC 630 with several fold advantages. First, a better suppressionof backflow is established. Second, at any given flow, the pressuregradient across process chamber 114 is reduced. Finally, the DGIC isbetter defined and the requirements for draw flow radial uniformity arerelaxed. However, in the embodiment of FIGS. 3 and 4, the range fornarrowing the gap between 804 and 205 which defines the conductance ofFRE 115 is limited by the need to provide a convenient path for wafertransport. However, in the embodiment presented in FIGS. 5 and 6, theconstraint of the wafer-loading path is removed with the implementationof a gap-controlling PSV. As illustrated in FIG. 5, the gap-controllingPSV implements a convex lower surface 880 on the bottom of a widerpoppet 856′ to narrow the gap 206 between 880 and chuck 205. Theresulting conductance of gap 206 can be as low as necessary since, asshown in FIG. 6, when the PSV is opened to facilitate wafer transport,gap-controlling surface 880 is raised and therefore does not interferewith the transport path. Gap-shaping portion 880 of PSV poppet 856′ ispreferably shaped with a down-looking substantially convex smoothcontinuation of part 804 to minimize flow disturbance.

To facilitate the gap-controlling PSV, the inner sealing gaskets andgasket grooves 872′ and 873′ are relocated as illustrated in FIG. 6.Likewise, top sealing surface 870′ is relocated.

In the PSV embodiment displayed in FIG. 3, crevices 882 and 884 next tosealing gaskets are effectively shielded from the ALD precursors by thehigh flow of inert gas in the DGIC. As taught above this is the crucialfeature that enables the implementation of, otherwise practicallyuseless, PSV for the SMFD ALD apparatus. However, in the gap-controllingPSV embodiment (FIG. 5), the gap of the inner seal is located insideprocess chamber 114 and therefore is no longer protected. Accordingly,entrapment of ALD precursors can adversely impact the memory of the ALDchamber and can lead to fast deterioration of the inner seal andrespective crevice if growth of inferior films in the gap is notsuppressed. To overcome this problem, the gap 882 must be purged with aslow flow of inert gas during chemical dose. FIG. 7 illustratesschematically the seal area of the PSV. Only the right side of across-sectional view is shown. Gap 882 between poppet 856′ and top 804′is purged through a delivery line 886 that is machined into the body ofpart 804′.

In another embodiment illustrated in FIG. 8, the inner seal of the PSVis completely eliminated and poppet 856′ forms a solid assembly with toppart 804″. Bellow 888 allows the entire assembly to elevate when theSemi PSV (SPSV) is moved to the OPEN position. In this case, purge gasconnection line 612 and the connections of chemical sources 105 and 105′(FIG. 1) are made flexible to accommodate an ˜12 mm of vertical motion.Accordingly, flexible hoses, bellows, or high purity Teflon linesections are implemented. It is appreciated that other means forretaining vacuum integrity while providing motion for 856″+804″ assemblycan substitute for the bellow seal shown in FIG. 8 without deviatingfrom the scope of this invention.

Another embodiment that is well-suited to eliminate the pitfalls ofcrevice 882 associated with the inner PSV seals is presented in FIGS. 9,10, 11, 12, and 13. In this embodiment, crevice 882 is protected by aninflated elastomer seal. The elastomer seal is made, for example, fromsuitable materials such as Viton, Kalrez, Chemraz, or equivalent and ismounted inside ledge 890 located under seal surface 870″. When the PSVis at the upper position (PSV OPEN), elastomer 892 is not inflated asshown in FIG. 9. When the PSV is at the lower position (PSV SHUT),elastomer 892 is inflated by applying inert gas or air pressure throughconduit 894. As a result, inflated elastomer 892 creates a seal againstan appropriately shaped surface on poppet 856′″. For example, FIG. 9depicts a concave shaped portion 889 of 856′″ that accommodates thecurved shape of inflated seal 892. Following this inflation, crevice 882is eliminated and only a small portion 896 of inflated seal 892 isexposed to the process (FIGS. 10 and 13). In one preferred embodiment ofthis invention, the inflated seal is made from a slightly permeableelastomer. Inflation with inert gas results in a slow flow of inert gasthrough the elastomer at exposed area 896. Accordingly, this inert gasflow suppresses the growth of films on exposed area 896 during process.In another alternative embodiment, the elastomer is appropriatelyperforated at the 896 area to provide a path for inert gas flow andprotection to area 896 from process chemicals.

Inflated elastomer seal 892 can be implemented in many different designsaccording to this invention. For example, FIGS. 11 and 12 illustrate aspecific preferred design. Part 804″ is split into an inner portion 898and an outer portion 900. Appropriately-shaped elastomer seal 892 isfolded and pressed between 898 and 900 and sealed into a substantiallytriangular-shaped tube by the pressure of upper and lower sealing ledges902 and 904, respectively (FIG. 11). Inflation path 906 is machined intoone or both of inner and outer parts 898 and 900 as depicted in FIG. 12.Against that path, elastomer 892 is appropriately shaped to conformaround a metallic ferrule 908. The pressure of sealing ledges 910 and912 seals the elastomer over ferrule 908 and in communication withinflation channel 906. Accordingly, an inflation/deflation path 914 iscreated. FIG. 13 displays a larger view of seal 892 after inflation.

In another embodiment SMFD ALD apparatus is implemented with a slidingliner that replaces the PSV in providing symmetrical and dead-leg freeALD processing space. FIG. 14 illustrates a preferred embodiment whereina radially shaped sliding liner is translatable to determine both thedraw control plenum and the DGIC. The sliding liner 940 is depicted inthe process position. In process position the sliding liner creates welldefined and well restricted flow paths 930 and 932 that are used todeliver the inert gas draw flow into DGIC 820 during chemical dose.During process the entire volume 934 behind liner 940 is pressurizedwith inert gas through inlet 830′. This volume includes the slit-valverelated cavity 922. Accordingly, a well-optimized draw flow plenum andFRE gap 206′ are established. In addition, a slit-valve cavity 922created by the interface with planar slit-valve 920 has no adverseimpact on the ALD process and is protected from the growth of inferiordeposits. When the chamber is set to facilitate wafer transport, thesliding liner is removed from the loading path 922 using actuator 858′while bellows 936 preserve the vacuum integrity of space 934.

The preferred SMFD ALD method implements liner 940 (FIG. 14) inconjunction with a sub-manifold that enables high-speed draw flowcontrol in spite of a substantial volume related to space 934. Forexample sub-manifold 960 depicted in FIG. 15 is used to vary thepressure within 934 quickly to facilitate fast variation of DC flow intoDGIC 630 (820 in FIG. 14). Preferably, the flow restriction of FRE 930and FRE 932 are selected to direct the majority of the draw control flowthrough FRE 930. When valve 120′ is shut, the booster volume 952 ispressurized to substantially reach the pressure at point 602. FRE 950 issubstantially less restrictive than FRE 121′. Accordingly, when valve120′ is opened the flow into space 934 resembles a high flow determinedby the flow through FRE 950 that levels off into a substantially lowerflow that is mainly dictated by FRE 121′. The high flow leading edgefacilitates quick pressure increase within space 934 to initiate fastturn “on” of draw control gas. To facilitate fast turn “OFF” of drawcontrol gas the combination of shutting valve 120′ off and openingevacuation valve 956 is implemented to quickly reduce the pressurewithin space 934. In the preferred method the evacuation valve 956 ismaintained open to reduce the pressure within space 934 down to apressure that is still slightly higher than the process pressure tofacilitate minimal flow of inert gas through both FRE 930 and FRE 932during purge. The design of liner 940 must comply with basic SMFD designrequiring that the pressure in the DGIC 630 will not be able to exceedthe pressure in the process chamber 114. This requirement set's an upperlimitation on the pressure rise rate within DGIC 630 not to exceed thetypical 34 msec residence time within ALD chamber 114.

SMFD advantageously lends itself to some simplified chemical sourceapparatuses and methods. In particular, the ability of SMFD to dosevaporized liquid and solid chemicals without a carrier gas is compatiblewith a simplified pressure-controlled chamber source where the vaporpressure of the chemical can be accurately controlled as described inthe exemplary embodiments below. Accordingly, the difficulty to controlthe partial pressure from chemical precursors in the flow of carrier gasis circumvented. Several different SMFD sources are depicted in FIGS.16, 17, 18, 19, 20, 21 and 22. Source chamber volume is chosen toimprove pressure-stability and to compensate for the slow response ofthe pressure control device or method that is typically limited withinthe 1-10 seconds range. Accordingly, it is advantageous to ensure thatsource chamber capacity (i.e., in liter×Torr) is substantially largerthan the material delivered per cycle. For example, source capacity thatis 20 times to 100 times larger than the capacity loss per dose lendsitself to a minimized pressure ripple in the source chamber, i.e., 316in FIG. 18, within 1% to 5%, which is tested to have indistinguishableimpact on the consistency and length of the chemical dose. Pressurecontrol devices cannot follow the speed of SMFD dose cycles. Rather, asdetailed herein, these pressure controlling devices or methods arepreferably set to control the average pressure in the source chamberwhile the capacity within the source is set to smooth out significantripples. Therefore, the volume of the source is chosen to limit pressurefluctuation, as necessary.

Several pressure control methods are described in FIGS. 16, 17, 18, 19,20, 21 and 22. In FIG. 16, a relatively high vapor pressure from liquidor solid chemical 306 is controlled by a commercially available pressurecontroller 312 such as the MKS Instruments 640A series which is limitedto operation temperature in the range from 0° C. to 50° C. The chemicalis located at a separate container 302 and is heated or cooled pertemperature control element 304 to provide a pressure, P_(chem), that islarger than the pressure that is needed in source 316. This pressure isfed into the inlet of pressure controller 312 that controls the pressureinside source chamber 316. A shut-off valve 308 is preferably placedbetween chemical container 302 and pressure controller 312 to terminatechemical supply through conduit 310 when processing is complete. Correctchoice of appropriate pressure controller and chemical temperatureensures stable and consistent chemical delivery. In particular, thechoice of pressure controller conductance must be suitable for thenecessary flow under given pressure conditions as known in the art anddescribed, for example, in the user manual of the 640A pressurecontrollers from MKS Instruments. The temperature of source 300,including gas line 310 interconnecting the chemical container with thepressure controller, pressure controller 312, the gas line 314interconnecting the pressure controller and source chamber 316, and gasline 318 interconnecting the source chamber with the SMFD-ALD manifoldat source points 105 and 105′ (FIG. 1) must be maintained at atemperature adequately high to prevent condensation of the precursorchemicals, as known in the art. Source evacuation is accomplishedthrough utility valve 320, conduit 322, and vacuum pump 324.

In another embodiment, 400, depicted in FIG. 17, consistent andcontrolled pressure from relatively non-volatile liquid chemicals isachieved by applying liquid delivery techniques to deliver the precursorwith precision into a vaporizing chamber. Vaporization chamber 406 isconnected to source chamber 402 through heated gas line 408. Thepressure is monitored at the source chamber using a conventionalpressure gauge 404 such as the model 628B or the model 631A Baratronmanufactured by MKS Instruments, which are suitable to reliably measurethe pressure of chemicals and can be maintained at temperatures of 100°C. and 200° C., respectively, to prevent condensation of non-volatilechemicals. Vaporized precursor is delivered to chemical source point 105through conduit 412. The entire assembly downstream from vaporizer 406is controlled at a temperature suitable to prevent condensation of thechemical. In certain embodiments, the temperature of vaporizer 406 iscontrolled separately and independently to improve vaporizationefficiency, speed, and control. Valve 416 is utilized to evacuate thesource chamber through conduit 418 and vacuum pump 420.

Liquid delivery control system 400 does not need to accommodate the ALDdose response, but rather to be able to sustain a consistent deliveryover a longer time scale. However, most commercially available liquiddelivery systems are not suitable to deliver such small quantities asrequired for ALD practice that are in the order of 10⁻⁴ cc/cycle. In thecase of SMFD with ˜2 cycles/sec, the liquid delivery system must be ableto precisely control flow on the order of 0.012 cc/min. This minutechemical flow is in the low range of, for example, top-of-the-lineDLI-25C system manufactured by MKS Instruments (low limit of 0.006cc/min). In addition, to maintain the volume of the source chamberconveniently small, the liquid delivery system must accommodate arelatively fast start/stop operation, preferably on the order of a cycletime which is difficult to achieve with commercially availabletechnology. An embodiment that accomplishes consistent delivery of smallliquid flow with fast response is described with respect to theschematic illustration given in FIG. 18.

Liquid delivery system 450 implements container 454 that is filled withliquid precursor 452 from chemical line 472 through inlet valve 470.Line 472 is connected to a liquid filling line (not shown) that drawsliquid precursor from a chemical reservoir such as the EpiFill systemfrom Epichem, Inc. A variable air chamber 456 completes the makeup ofcontainer 454 with a flexible bellow 458. The liquid can be pressurizedby introducing air from pneumatic line 464 through valve 462 into airchamber 456 to force chamber 456 to expand downwards and pressurize theliquid. The liquid can be depressurized by evacuating the pressurizedair out of chamber 456 through valve 466 into line 468. Accordingly, theliquid can be pressurized and depressurized within 5 msec to 50 msecwith standard solenoid valves. Variable orifice 460, for example, aproportional valve, is used to set the flow of liquid towards outlet 410when the liquid is pressurized. When metallic bellow 458 approachesmaximum extension, container 454 is automatically refilled. For example,bellow 458 approaches the bottom of container 454 where a magneticproximity sensor is mounted. A magnet inside chamber 456 is sensed atproximity and the system will refill container 454 within the next idletime. The proximity sensor is designed to sense the need for refill whensystem 450 is still capable of delivering enough chemical for an entireinterval between idle times. Alternatively, two liquid delivery systems450 may be connected to a single source 400 and alternately serve andrefill. Refilling is accomplished by depressurizing chamber 456 andpushing liquid through valve 470 to retract bellow 458 and refillcontainer 454.

Solid chemicals present several source design challenges. In particular,the inconsistency of evaporation rate from solid chemicals due tofluctuation in the area of the solid material makes seeding vapors fromsolid source into carrier gas expensive and unreliable. In addition,thermal contact of solid chemicals usually in a shape of fine-grainpowders is typically poor leading to significantly inefficient and slowsublimation rates. Accordingly, it is very difficult to maintainconsistent and non-depleted supply of vaporized molecular precursorsfrom solid sources. This difficulty applies for both pure vapor form oras partial pressure within a carrier gas.

An embodiment 700 disclosing a vapor source from solid chemicals isdescribed here with reference to FIG. 19. The source implements atechnique to monitor the condensation rate of condensable materials forindirectly evaluating the vapor pressure of this condensable materials.A temperature controlled sensor 710 senses the accumulation of materialson it's sensing surface 711. Sensor 710 is preferably a Quartz crystalMicrobalance (QCM), a Surface Acoustic Wave (SAW) device sensor, orother thickness monitoring devices or techniques. Sensor 710continuously indirectly probes the vapor pressure of the molecularprecursor in the following manner: The molecular precursor is sublimatedusing resistive heating or other suitable means to maintain a minimalgrowth rate of condensed film of molecular precursor on the materialaccumulation sensor, e.g. a QCM in the preferred embodiment.Hereinafter, a QCM is used as the exemplary sensor, though it should beunderstood that other sensors can be used. The QCM sensor is preventedfrom having a line-of-sight with the sublimation source and thereforethe growth of condensed film on it represents condensation of excessivevapor pressure. The temperature of the entire source, 708, with theexception of the QCM sensor is maintained sufficiently high to preventcondensation at the desired precursor vapor pressure. Commerciallyavailable QCM sensor heads are capable to control the deposition orcondensation of films on their exposed area with a rate typically betterthan 2% of a monolayer per second. To facilitate the desired vaporpressure, the temperature of the QCM sensor is maintained by a sensortemperature control system 713 at a pre-selected temperature. Thepre-selected temperature for the sensor is several degrees lower thanthe condensation temperature of the molecular precursor at the desiredcontrolled vapor pressure. Accordingly, by controlling the sublimationsource to sustain a minimal condensation rate on the QCM sensor themolecular precursor is maintained at a desired,substantially-controlled, vapor pressure. Commercially availabledeposition controllers and sublimation sources are proven to be able toreach well-controlled deposition rates within several seconds.Accordingly, source 700 is capable to go from a standby mode wherein thevapor pressure of the molecular precursor is insignificant to a processmode wherein the desired precursor vapor pressure is maintained insidethe source within several seconds. Source 700 is also capable toreplenish the molecular precursor in the source on a time-scale ofseveral seconds. Accordingly, a source with a well designed capacitythat accommodates only minor pressure drop during ALD dose, as describedabove, is well suitable for high-productivity ALD applications. Withonly seconds required to cross from idle source with negligible vaporpressure to “active” source with appropriately controlled vapor pressurethe source is practically set to idle in between successful waferprocessing. During a typical semiconductor wafer processing of 3 minutesor less the condensation on the QCM will accumulate only severalmonolayers. This negligible thickness will be sublimated away from theQCM surface during idle mode.

Source chamber 702 is connected to source point 704 (equivalent to 105and 105′ in FIG. 1) through an appropriately heated conduit (not shown).The volume of source chamber 702 is chosen to reduce pressurefluctuations and to accommodate the capabilities of commerciallyavailable deposition controllers and sensors as described above. Thesource is equipped with a temperature controlled QCM sensor 710 having asensing area 711. For example the BSH-150 Bakeable sensor head availablefrom Maxtek, Inc. that is proven to work reliably in the temperaturerange from 30-300° C. The temperature of sensor 710 is tightlycontrolled using a combination of resistive heating and air-flowcooling. Preferably the temperature of the sensor 710 is controlledwithin better than ±0.1° C. to suppress sensor fluctuations and drift.Sensor 710 is preferably modified to seal access to the back side of thequartz crystal microbalance using, for example, Viton cement or othercomplying adhesives with high temperature compatibility as well ascommercially available high temperature elastomer seals such as KalrezO-rings or equivalents.

Sensor 710 is monitored by deposition controller 716 such ascommercially available MDC360C from Maxtek, Inc. or the IC/5 controlleravailable from Inficon. The QCM is capable of measuring thickness withbetter than 0.1 Å resolution that is equivalent to better than 4% of amonolayer of most materials. Likewise, commercially available depositioncontrollers are capable of controlling the power to evaporation sourcesto maintain a selected deposition rate with as low as 2% of a monolayerper second.

Source 702 is also equipped with an evaporation/sublimation source 722.For example resistively heated crucible 722 containing a powder ofmolecular precursor 724 such as HfCl₄. The sublimation source is mountedwithin source 702. Electrical-current feedthroughs 720 are used to feedpower to provide quick heating of crucible 722. Commercially availablecrucibles are proven to be able to initiate well controlled thermalevaporation/sublimation of various materials within a time scale ofseconds when feedback controlled to sustain a preset reading on adeposition rate sensor such as sensor 710. For example the feedback loopschematically illustrated in FIG. 19 with comparator 728, control lines718 and 726 and set-point 730. In the case of chemical source 700,sensor 710 preferably does not have a line of sight with the vaporsemerging from sublimation source 722.

Source 700 also includes a refill valve 734 and a refill conduit 732. Toreplenish the source chemical, for example HfCl₄ powder, the powder ispreferably immersed within an inert liquid to generate a slurry. Thechemical is loaded into an idle, vented and preferably cold (i.e. roomtemperature) source 700 from point 736 by opening valve 734. Followingthe delivery of a metered amount of slurry valve 734 is flush withsufficient amount of inert liquid to flush the powder from the valveprior to shutting the valve off. The source is then evacuated and theinert liquid is subsequently evaporated using vacuum pump 742 throughvalves 734 and 740 and line 738. For this operation slurry-sourcemanifold and vent manifold that are connected at point 736 are isolatedusing appropriate shut-off valves (not shown). During inert liquidevaporation the sublimation source may be slightly heated to promoterapid removal of the liquid.

The solid material is preferably introduced as a thoroughly mixed slurryof fine powder solid chemical with an inert, highly volatile liquid suchas freon, carbon tetrachloride (CCl₄), trichloroethylene, or Galden HT55from Solvag Solexis, to name a few alternatives. The liquid is used toshield the precursor from ambient exposure during transfer since mostprecursors react violently with moisture and/or oxygen. A slurry isbetter suited than a solvent since it is more generic. In addition,solvated precursor can still react with the ambient while wet, andimmersed solid particles in a slurry are practically isolated fromcontact with the ambient. A slurry is also easier to dry-out completelyfrom all trace of liquid.

The source 700 illustrated in FIG. 19 can appropriately control thepressure of a solid as well as liquid chemical with consistency that iswell suited for ALD. In another embodiment, source 700′ that isillustrated in FIG. 20 controls both the partial pressure of a solidprecursor or a liquid precursor as well as the total pressure ofprecursor diluted within inert carrier gas. For this purpose the partialpressure of precursor is maintained and feedback controlled using thecombination of sensor 710 and sublimation/evaporation source 722 and anappropriate deposition controller 716 as described above with referenceto source 700 in FIG. 19. In addition, high-temperature pressure gauge706 and valve 744 are used to deliver inert gas from inert gas manifold746 to maintain source volume 702 at a controlled total pressure.Shutoff valve 744 is feedback controlled to maintain set-point totalpressure 750. Alternatively, high temperature proportional valve incombination with shutoff valve 744 may be used. The total pressure iscontrolled to exceed the vapor pressure from the chemical. Since theadditional gas in not condensable at the temperature of the QCM, the QCMis able to control the partial pressure of the chemical independent ofthe total pressure.

Source 700′ advantageously allows to prepare and sustain a wellcontrolled mixture of reactive chemical vapor seeded into inert carriergas wherein both the partial pressure of the precursor and the totalpressure are independently controlled. In addition, source 700′ can beused for in situ preparation of precursor. Accordingly source 700′ isoperated in an etch mode wherein the gas supplied from manifold 746contains an etch gas such as Cl₂, Cl₂/O₃, HF etc. or a well-optimizedmixture of etch gas with inert gas. The sublimation source 722 containsa metallic powder or otherwise a compound suitable for effectivegeneration of volatile etch product (such as RuO₂ suitable to generateRu(VIII) oxide or ruthenium oxichlorides). The temperature of crucible722 is controlled to promote efficient reaction of etch gas with thetarget material 724 to generate the desired molecular precursor. Usingthis method eliminates the need to handle and contain hazardouschemicals within source 700′ and in the slurry manifold. In addition,metallic sources are usually available at substantially higher puritythan compound chemicals and at substantially lower cost. Additionaladvantage comes from the ability to generate metastable precursormolecules which are otherwise difficult to store such as theoxichlorides of Ta, Nb, W, Hf, Zr, Ru etc. as well as volatileprecursors that are unstable and extremely hazardous such as RuO₄. Forexample, HfCl₄ may be generated from the combination of Hf powder withincrucible 722 and a mixture of Cl₂/N₂ delivered from 746. The temperatureof 722 is controlled to satisfy a low condensation rate of HfCl₄,clearly the most volatile etch product, on sensor 710. In an alternativemethod the precursor HfOCl₂ is generated from metallic Hf in 722 and amixture of Cl₂/O₂/O₃ coming from manifold 746. In this case the volatileHfOCl₂ will be the dominant etch product at sufficiently high ratio ofO₃/Cl₂. In yet another example RuO₄ is generated from RuO₂ loaded into722 and O₂/O₃ delivered from manifold 746. In yet another example,volatile carbonyl molecules such as W(CO)₆ are prepared using W powderand CO gas.

In alternative embodiment source 700′″ illustrated in FIG. 21 implementsan alternative sublimation source 770 using metallic target 722 shapedas a wire (shown), rod, plate, foil etc. wherein the sublimation ofin-situ prepared precursor from etching target 772 is promoted byrunning direct heating current through target 772 from transformer 778that is controlled to maintain the desired low condensation of theprecursor on sensor 710. In the configuration shown in FIG. 21 a highpurity wire 772 is clamped using high purity metallic clamps 774.

FIG. 22 presents another exemplary embodiment wherein source 700′″ doesnot include a pressure gauge to control the total pressure within source700′″ internal volume. Reliable pressure gauges such as the MKS 631A areavailable and can withstand harsh chemicals and temperature up to 200°C. These gauges are well suited for sources such as in 700′ (FIG. 20)and 700′ (FIG. 21). However, in some cases sources temperature exceeding200° C. may be desired. In addition, the combination of high-temperatureand corrosive chemicals may accelerate drift and failure of pressuregauges such as the MKS 631A or the MKS 628B. Additionally, hightemperature pressure gauges are rather expensive. In the alternativeapproach of FIG. 22 the total pressure is indirectly maintained byproviding a well pressure controlled reservoir 780 upstream to valve744′. The volume of reservoir 780 is sufficiently large to sustain wellregulated pressure with the aid of an off-the shelf pressure controller782 such as the MKS series 640A devices. The gas is fed at point 746′and maintained within reservoir 780. Following the completion of a dosefrom source 700′″ the total pressure is replenished by opening valve744′ for a duration sufficiently long to substantially bring thepressure within 700′″ internal volume to the pressure that is controlledwithin 780. Preferably, the opening of valve 744′ is not timedexcessively long to avoid diffusion of non-volatile precursor upstreamof valve 744′ where the temperature is not sufficiently high to preventcondensation. While the sublimation source shown in FIG. 22 resemblesthe source of FIG. 21 it is understood that the method for totalpressure maintenance taught with reference to FIG. 22 is suitable forthe embodiments and method that were presented in reference to FIG. 20and their derivatives such as direct sublimation or in-situ precursorgeneration, as well.

The apparatuses for in-situ generation of precursors using the methodthat was described in reference to FIG. 20, FIG. 21 and FIG. 22 issuitable to prepare desired compound precursor molecules that aresubstantially more volatile than the pure element or other undesiredcompounds. Many different precursors can be prepared with substantialadvantages ranging from stability, safety, consistency, purity and cost.Several examples are given below (for simplicity, the equations are notbalanced):Hf+Cl₂→HfCl₄↑  (1)RuO₂+O₂+O₃+Cl₂→RuO_(x)Cl_(4-x)↑  (2)W+Cl₂→WCl₆↑  (3)Ru+CO→Ru₃(CO)₁₂↑  (4)Mo+Cl₂→MoCl₅↑  (5)

Systems, apparatuses, and methods designed and operated in accordancewith the invention are particularly useful in ALD technology.Synchronous modulation of flow and draw, SMFD, is also useful, however,in a wide variety of circumstances and applications. It is evident thatthose skilled in the art may now make numerous uses and modifications ofthe specific embodiments described, without departing from the inventiveconcepts. It is also evident that the steps recited may, in someinstances, be performed in a different order; or equivalent structuresand processes may be substituted for the structures and processesdescribed. Since certain changes may be made in the above systems andmethods without departing from the scope of the invention, it isintended that all subject matter contained in the above description orshown in the accompanying drawings be interpreted as illustrative andnot in a limiting sense.

1. A chemical source vapor pressure control system comprising: achemical source chamber, a chemical source holder within said chemicalsource chamber for holding a solid or liquid chemical source, a chemicalsource heater, a source heater controller, and a deposition accumulationsensor, said heater controller electrically connected to said depositionaccumulation sensor to control the heating of said source, saidtemperature controlled deposition accumulation sensor located out ofline-of sight with said chemical source while it is electricallyconnected to said heater controller; and a sensor temperature controlunit for controlling the temperature of said accumulation sensor to atemperature substantially equal to the condensation temperature of thechemical source at the desired vapor pressure.
 2. A chemical sourcecontrol system as in claim 1 wherein said source chamber has chamberwalls and further comprising a chamber wall temperature control systemfor maintaining said walls at a temperature that is sufficiently high toprevent condensation of said chemical source.
 3. The chemical sourcevapor pressure control system as in claim 1 and further characterized bya pressure gauge, a gas control valve, and a pressure controllerconnected between said gauge and said valve to control the totalpressure within said source chamber to a pressure higher than saidcontrolled vapor pressure of said chemical source.
 4. The chemicalsource vapor pressure control system as in claim 1 and furthercharacterized by a source of an etch gas connected to said gas controlvalve, and said sensor senses a condensable chemical which is an etchingproduct.
 5. The chemical source vapor pressure control system as inclaim 4 and characterized in that said chemical source is selected fromthe group consisting of Hf, Zr, Ru, RuO₂, Si, W, Mo, Co, Cu, Al, Os,OsO₂, Fe, Ta and combinations thereof; and said etching gas is selectedfrom the group consisting of Cl₂, Cl₂/N₂, Cl₂/O_(2/O) ₃, N₂/HF, N₂/CIF₃,CO, CO/N₂ and combinations thereof.
 6. The chemical source vaporpressure control system as in claim 1 wherein said vapor control systemis part of an atomic layer deposition (ALD) system and furthercharacterized by a pressure controlled reservoir; a shutoff valve inseries fluidic communication between said pressure controlled reservoirand said source chamber to substantially equalize the pressure betweensaid source chamber and said pressure controlled reservoir betweensuccessive ALD doses.
 7. The chemical source vapor pressure controlsystem as in claim 1 wherein said source is applied for ALD and thecapacity of said source chamber is 20 times or more larger than thecapacity required for a single ALD dose.
 8. A method for controlling thevapor pressure of a solid or liquid chemical source within a sourcespace said method comprising: sensing the accumulation of said chemicalon the sensing surface of an accumulation sensor; controlling thetemperature of said chemical source depending on said sensedaccumulation to control said vapor pressure; and controlling the totalpressure in said source space to be higher than said vapor pressure ofsaid chemical by adding a non-condensable gas to said source space.
 9. Amethod as in claim 8 wherein said temperature of said chemical source iscontrolled to maintain a minimal measurable condensation rate on saidsensing surface.
 10. The method of claim 8 and further characterized bycontrolling the temperature of said sensor to determine the desiredvapor pressure of said chemical.
 11. The method of claim 8 and furthercharacterized by introducing an etching gas into said source space; andetching an elemental or compound target to produce said chemical.